Described herein are radiation curable phase change ink compositions ideally suited for use in ink jet ink printing devices. In embodiments, the ink includes a curable gellant additive along with a colorant. The ink vehicle may also contain additional curable components, along with an initiator for curing upon exposure to radiation.
The volume of digital color printing is expected to experience significant growth in the coming years. The color images provided by ink jet printing inks are overwhelmingly preferred in panel studies over other digital imaging systems. There is also a strong case to be made that the total cost of ownership of an ink jet printer will ultimately be cheaper than similar volume electrophotography units.
Ink jetting devices are known in the art, and thus extensive description of such devices is not required herein. As described in U.S. Pat. No. 6,547,380, incorporated herein by reference, ink jet printing systems are generally of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium. There are three types of drop-on-demand ink jet systems. One type of drop-on-demand system is a piezoelectric device that has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as acoustic ink printing. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands.
In a typical design of a piezoelectric inkjet device, the image is applied by jetting appropriately colored inks during four to six rotations (incremental movements) of a substrate (an image receiving member or intermediate transfer member) with respect to the ink jetting head, i.e., there is a small translation of the printhead with respect to the substrate in between each rotation. This approach simplifies the printhead design, and the small movements ensure good droplet registration. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Hot melt inks typically used with ink jet printers have a wax based ink vehicle, e.g., a crystalline wax. Such solid ink jet inks provide vivid color images. In typical systems, these crystalline wax inks partially cool on an intermediate transfer member and are then pressed into the image receiving medium such as paper. Transfuse spreads the image droplet, providing a richer color and lower pile height. The low flow of the solid ink also prevents show through on the paper.
In these systems, the crystalline wax inks are jetted onto a transfer member, for example, an aluminum drum, at temperatures of approximately 130-140° C. The wax based inks are heated to such high temperatures to decrease their viscosity for efficient and proper jetting onto the transfer member. The transfer member is at approximately 60° C., so that the wax will cool sufficiently to solidify or crystallize. As the transfer member rolls over the recording medium, e.g., paper, the image comprised of wax based ink is pressed into the paper.
However, the use of crystalline waxes places limitations on the printing process. First, the printhead must be kept at about 130° C. during the print process. Moreover, when the printhead is cooled and re-warmed, the resulting contraction and expansion of the ink requires a purge cycle to achieve optimum printhead performance. Furthermore, increased mechanical robustness is desired.
Recently, Xerox has discovered several radiation curable inks that may be jetted at much lower temperatures and that achieve robust images following curing. Reference is made to the following patent properties, each of which is incorporated herein by reference in its entirety. (1) Co-pending application Ser. No. 11/034,850 entitled “Low Level Cure Transfuse Assist for Printing with Radiation Curable Ink”; (2) Co-pending application Ser. No. 11/034,856 entitled “Ink Jet Ink Curable Via Different Polymerization Routes”; and (3) Co-pending application Ser. No. 11/034,714 entitled “Ink Jet Ink of Functionalized Waxes”. U.S. Pat. Nos. 6,561,640 and 6,536,889, each incorporated herein by reference in its entirety, describe processes of forming ink jetted images using UV curable inks.
U.S. Pat. Nos. 5,804,671, 5,889,076, 6,239,189 and 6,316,517, as well as U.S. Publication No. 2003/0036587, each disclose compositions including rheology modifying agents therein. U.S. Pat. Nos. 5,804,671 and 5,889,076 describe a composition that is useful in the preparation of radiation curable coatings and comprising the reaction product of an epoxy component and an acid component comprised of an ethylenically unsaturated carboxylic acid or reactive derivative thereof, reacted in the presence of, or post-reaction blended with, a polyamide based on a polymerized fatty acid and having a number average molecular weight of less than about 10,000 g/mole. U.S. Pat. No. 6,239,189 describes a radiation-polymerizable composition that may be including in a printing ink, the composition containing at least one curable acrylate resin oligomer prepared by reacting an alkoxylated polyol with a first acid component which includes an ethylenically unsaturated carboxylic acid, and a rheology modifier prepared by reacting a diepoxide with a second acid component which includes an ethylenically unsaturated carboxylic acid or reactive derivative thereof in the presence of a polyamide based on a polymerized fatty acid. Ink jet inks and/or phase change inks are not described, and in fact it is believed that the viscosities of the inks described in this reference would be so large that such inks could not be jetted. U.S. Pat. No. 6,316,517 describes radiation-polymerizable compositions that are especially useful as or in a flush vehicle for making flushed pigments. The compositions contain at least one radiation-curable acrylated resin component and a copolymerizable rheology modifier component. In particular, the flushed pigment comprises a pigment and a flushing vehicle, the flushing vehicle comprising a substantially homogenous admixture of two or more curable acrylated resins selected from the group consisting of acrylated epoxies, acrylated urethanes and acrylated polyesters, and a rheology modifying resin copolymerizable with curable acrylate resin when subjected to radiation in the presence of a photoinitiator, for example the reaction product of (i) an epoxy component, (ii) an ethylenically unsaturated carboxylic acid or reactive derivative thereof and (iii) a fatty acid or reactive derivative thereof, said components (i), (ii) and (iii) being reacted in the presence of a polyamide based on a polymerized fatty acid. U.S. Publication No. 2003/0036587 describes a rheology controlled epoxy composition capable for use in bonding a silicon substrate to a flex circuit or a flex circuit to a pen body, comprising: (a) an epoxy resin component; (b) a rheology control agent selected from the group consisting of epoxysilanes, aminosilanes, trialkoxysilyl isocyanurate derivatives, and combinations thereof; (c) a curing agent component comprising a member selected from the group consisting of amine compounds, amide compounds, imidazole compounds, and combinations thereof; and (d) optionally, an inorganic filler component.
U.S. Pat. No. 6,586,492 describes an ink-jet ink comprising an ink jet vehicle and a colorant, the vehicle comprising at least 35% by weight, based on the total vehicle weight, of a radiation curable material and further comprising a thickener, said vehicle being a thixotropic paste at 20° C., and said vehicle having a viscosity of less than 25 centipoise at least at one temperature in the range of from 40° C. to 130° C.
U.S. Pat. No. 5,892,116 and PCT Patent Publication WO 97/24364, the disclosures of each of which are totally incorporated herein by reference, disclose gellants that gel a variety of nonpolar and polar liquids. Moreover, gelation of various monomers with subsequent polymerization of the gelled monomers forms organic zeolites and membrane materials.
While known compositions and processes are suitable for their intended purposes, a need remains for improvements in radiation curable inks, for example with respect to jetting temperatures, fusing latitude and image quality.